The shafts of weaving machines are moved very rapidly during weaving and are induced to oscillate. This applies generally, but it may lead to particular problems in case of long shafts (wide fabrics). The shaft oscillations are generated both parallel and transversely to the longitudinal direction of their motion. The oscillations lead to stresses on the heald shaft, the healds, the heald staves and the warp treads. The stresses may cause premature heald breakage, shaft breakage or other defects.
It has already been repeatedly attempted, on the one hand, to reduce the weight of the shaft rods to lessen the generation of oscillation and, on the other hand, to increase the rigidity of the shaft rods. These efforts have resulted in improved shaft rods, while, as before, the purpose of further development has been to increase the obtained limits for the working speed of the weaving machine and to improve the accuracy of thread guidance, that is, as an ultimate goal, to reduce the amplitude of the bending oscillations of the shaft rods.
The tendency of the shaft rods to oscillate significantly contributes to the noise generation and wear of the weaving machines. Also, as concerns noise reduction, it is a purpose in developing heald shafts to reduce their tendency to oscillate.
German Patent Document No. 29 43 953 C2 describes a heald shaft rod having a light-metal, hollow-chamber profile. The heald shaft rod has two flat side walls which enclose several hollow chambers. One of the side walls is glued to a steel band extending almost along the entire height of the side wall for the purpose of reducing oscillations of the shaft rod to thus diminish the generated sound intensity.
Possibilities concerning a damping of oscillations are explored for the purpose of surpassing the effectiveness of the above-outlined measure.
German Patent Document No. 39 37 657 A1 discloses a shaft rod which is formed by a two-part profiled aluminum body. The two aluminum profiles together enclose a total of three hollow chambers, of which one chamber is filled with a foam body and the other two chambers are filled with a synthetic carbon fiber body. The synthetic carbon fiber bodies have an approximately rectangular cross section which entirely fills the respective hollow chamber. The synthetic carbon fiber bodies are glued by means of an epoxy resin adhesive to the two side walls of the hollow chamber profile and to the contacting webs thereof.
The positioning of the synthetic carbon fiber bodies in chambers which are closed on all sides and which are formed between the two mutually fitting aluminum profiles requires an accurate fit between the two aluminum profiles themselves and the synthetic carbon fiber parts. This requirement constitutes a significant manufacturing difficulty. Furthermore, the shaft rod has an appreciable weight.
A shaft rod also provided with an integrated stiffening is known from German Patent Document No. 36 21 145 A1. The shaft rod is formed by two elongated, mutually fitting parts which together close an inner space filled with a stiffening element and a honeycomb element. The stiffening element is formed by a carbon fiber body.
The positioning of the carbon fiber body into the closed inner space involves not only manufacturing difficulties, but also leads to a significant weight of the shaft.
U.S. Pat. No. 3,754,577 describes a shaft rod formed as a hollow-chamber profile. According to one of the embodiments the shaft rod is, at its upper edges as well as at its lower edges, provided with apertures into which stiffening elements of rectangular cross section are glued. While the hollow-chamber profile is of aluminum, the stiffening elements are made of a fiber glass reinforced synthetic material.
Shaft rods of the above-outlined construction have an increased stiffness with respect to stresses which act in the directions of motion, that is, parallel to the side walls of the profiled body. Oscillations which are transverse to the shaft profile, however, are damped to a lesser degree. In this respect a shaft rod of such a construction too, is considered to be in the need of improvement. Such considerations also apply to German Utility Model No. G 69 29 985 which discloses a similar shaft rod.
Accordingly, it is an object of the invention to provide a heald shaft, particularly for rapidly operating weaving machines, which has a greater dynamic stiffness and better oscillating properties than prior art constructions.